Satele Force pasted Malgus to a rock
Tol Braga...yeah, you are right
Orgus is aging, that's why he lost, plus he didn't go intending to fight
Bela Kiwiiks...well, we don't know much about her fighting skills, I'd bet she's a consular
Syo Bakarn, to be fair he hasn't even been seen in combat aside from his "other" personality
Jun Seros and Kellian Jarro lost to the best bounty hunter in the galaxy
She pasted Malgus to a rock after Jace Malcom blew a thermal detonator in his face, she was losing the fight long before that, she even admits this.
Orgus actually lost to Angral during the Sacking of Coruscant, there he did go to fight and he barely escaped afterwards.
I give you that Seros and Jarro did lose to the best bounty hunter in the galaxy but hes still just that, a bounty hunter. Not a powerful sith, but a bounty hunter. Granted he could take on and beat most sith, but all bounty hunters/Mandalorians (Jango Fett, Pre Visla) will get beat by more powerful sith/jedi eventually.